Driving Question: How can we design a device to pasteurize water using the sun and cheap materials that can be found in impoverished countries?
According to the World Health Organization (WHO), between 2 million and 5 million people—many of them children in developing countries—die each year from diseases resulting from contaminated water. Your team has been hired by WHO to help solve this major world health crisis. Your challenge is to design the most efficient, inexpensive, portable solar cooker that will attain a temperature needed to pasteurize contaminated water and make it healthy to drink. Criteria for Success The effectiveness of your cooker will be judged by • its efficiency (pasteurizing water the fastest) • its cost-effectiveness (uses inexpensive materials) • its portability (can be easily transported from one place to another)
The first step in any invention process is identifying a need or want for something—in this case it is an inexpensive and environmentally safe way to cook food. One solution to that, the one you will be exploring in this activity, is to research and build a portable, inexpensive solar cooker that can heat water quickly. Use these steps to help guide your invention process. Step 1—Conduct Research: Use print and Internet resources to investigate solar cookers, particularly the type you will be building, a passive solar cooker. There are primarily three types of passive cookers: box cookers, panel cookers, and parabolic cookers. From your research, come up with a list of solar cooker characteristics that will help you meet your criteria for success. Brainstorm a list of materials that you think may optimize the type of cooker you will be designing and building. Step 2—Develop a Plan: As a team, choose the materials you want to use to design and build your solar cooker. As you think about which design you would like to use, consider how to most effectively use your materials to concentrate the sun's energy to heat your water. Step 3—Design Your Model: Develop a drawing of your design model. The drawing should indicate the cooker's parts, dimensions, and materials to be used. Consider how you are going to use your thermometer to measure the temperature (if you have to keep opening your cooker to put in the thermometer, the temperature will drop).
Step 4—Build Your Model: Build your model. As you build it, make sure to include detailed notes in journal form about the final shapes, dimensions, and materials used to construct the actual cooker. These will help you later evaluate the cooker's performance. Step 5—Test Your Model: You will test your model outside with a cup of water. You will use a temperature probe to plot the temperature change over time, note when you have reached 65° C. Step 6—Revise and Retest Your Model: Identify the strengths and weaknesses of your current model. Make any modifications you think will improve the efficiency of your solar cooker. Note the changes you decided to make to your prototype on your original drawing and include in your team journal why you decided to make those changes. Retest your model. Step 7—Evaluate Your Invention: Compare the efficiency of your first solar cooker to your second design through answering analysis questions. Then compare your design with those of other teams in your class. As a class, compare and discuss each team's final design and effectiveness in meeting the criteria for success.
Questions: Type your answers on a separate sheet of paper. 1. Based on your data, was your first model or your redesigned model more efficient at heating the water? 2. What factors do you believe accounted for the differences in the efficiency of the two solar cooker designs? 3. List three variables that affect the time it takes to heat water in a solar cooker. 4. Draw a diagram to show how transmission, reflection, absorption, and insulation played a part in your solar cooker (depending on your type of cooker not all of these concepts may apply). 5. If you had to change one design element in your cooker to improve it for a last test, what would it be? Why would you make the change? 6. Compare the use of the sun as an energy source to one of the following types of energy sources: wood, fossil fuels such as coal or oil, nuclear power, wind, or water.